1. Technical Field
The present disclosure relates to a method for evaluating corrosion-fatigue properties of steel materials used under corrosive environment.
2. Related Art
Generally, the corrosion-fatigue life of a steel material is evaluated as the time when a crack is generated in a predetermined portion that is in contact with a corrosive medium under cyclic loading. For example, the number of crack generation cycles is measured as a numerical index for evaluating the life. In a strict sense, the “number of crack generation cycles” is defined as follows: If cyclic loads are applied to a steel material under corrosive environment, a crack is generated in the steel material. The number of cyclic load applications (the number of cycles) at the time of crack generation in the steel material is referred to as the “number of crack generation cycles”.
Procedures used for the evaluation are described in, for example, patent documents JP-A-2010-107372, JP-A-48-075086, and JP-U-63-088739. The method described in JP-A-2010-107372, cyclic loads are applied to the surface of a test specimen having a corrosive medium introduced into a space formed inside the test specimen. The corrosion-fatigue damage is then evaluated. JP-A-48-075086 proposes a corrosive liquid tank for conducting a fatigue test under corrosive atmosphere. A columnar fatigue test specimen is attached to the corrosive liquid tank. A loading mode is axial force. Moreover, JP-U-63-088739 proposes a stress corrosion cracking test apparatus. This apparatus includes means for applying a tensile load to a test specimen based on a measured stress value by a strain gauge. In the corrosion-fatigue test, cyclic loads are applied to a test specimen under the environment of a corrosive medium. In the measurement of the number of crack generation cycles, generally, the corrosion-fatigue test is conducted two or more times to improve the reliability of the measured values. The number of crack generation cycles is obtained as, for example, the average value of the plurality of obtained measured values.